a) Field of the Invention
The present invention relates to a vacuum processing apparatus, and more particularly to a vacuum processing apparatus for processing a workpiece by introducing processing gas into a vacuum chamber.
b) Description of the Related Art
Impurity gas in a process chamber of a vacuum processing apparatus such as a vacuum sputtering apparatus has been detected heretofore with a mass analyzer mounted in the process chamber, through differential evacuation of the inside of a sensor of the mass analyzer. Alternatively, a mass analyzer is mounted on a cryopump for evacuating the inside of a process chamber to measure a partial pressure of impurity gas. Abnormal states such as leakage of the vacuum apparatus can be detected by measuring the amount of impurity gas.
A mass analyzer typically uses an amplifier such as a secondary electron multiplier for amplifying small ion current. As the mass analyzer continues to measure gas partial pressure for a long time, the gain of the secondary electron multiplier lowers because of contaminant attached to the secondary electron multiplier or native oxide films or the like formed on the secondary electron multiplier, or the position of a peak detection signal of each mass may shift from a normal position on the mass number coordinate axis.
Such a lowered gain of the secondary electron multiplier or a position shift of a peak detection signal makes difficult to correctly measure a partial pressure of impurity gas.
The partial pressure of impurity gas fluctuates with time. A partial pressure measured with a mass analyzer is an instantaneous value. Therefore, even a momentary abnormal value of a gas partial pressure which does not substantially affect vacuum processing may be detected as an abnormal state of the vacuum processing apparatus.